The production of such composite bodies has been carried out heretofore in a number of different ways generally in a number of successive operations. The bodies have the advantage that they can be composed of a low-density core material, filler or the like, but are protected by a high density substantially fluid-impermeable skin which provides a smooth external surface of esthetic and protective value.
Such bodies are used in the production of cushions, furniture, vehicle-dashboard linings, padding etc.
One obvious technique for producing such bodies is to blow a parison of the thermoplastic synthetic-skin material into a mold and thereafter inject the core material which can be permitted to foam in situ. In another technique, the core material may be introduced first and a layer of the skin material can be introduced subsequently between the foamed core and the wall of a slightly larger mold cavity.
All of these systems and others which have been proposed have various disadvantages which have prevented widespread use in an economical manner. Some of the problems include reproducibility of the product, uniformity of the coating or density of the core material, etc.